1. Field of the Invention
The present invention relates to a camera having a photographic optical zoom system, and especially to the driving mechanism of the optical photographic zoom system.
2. Description of the Related Art
Some cameras include an optical zoom system (zoom lens), i.e. a photographic optical system (photographic lens) that has a zooming function with which the focal length can be changed within a certain range. Many single lens reflex cameras are adapted to receive removable, and hence exchangeable, photographic lenses, while most compact cameras carry a photographic lens that has been mounted during production and is not removable or exchangeable. Therefore, many compact camera users select a camera having a zoom lens with a magnification range that meets their purpose and preference on purchase.
In most cases, the zoom lens has its focal length changed when the user pushes down a button to shift the lens barrel that holds the lens. When not in use, many zoom lenses are positioned at the barrel retracted position in which the lens barrel is retracted in the camera body.
When the camera is turned on, the lens barrel of the zoom lens comes out of the barrel retracted position. The zoom lens barrel stops within a zoom range that is defined by the zoom lens specification as a range of focal length in which photographs can be taken. At this point, the camera is ready to take pictures.
In many cases, the zoom lens barrel is initially set in the wide-angle position when the power is turned on. When the camera is ready for taking photographs, the lens barrel can be moved to change the focal length of the zoom lens by the operator pushing down a button. The lens barrel may move within the zoom range after the camera has been ready to take pictures, and is controlled not to move beyond the boundaries of the zoom range or the zoom limits. The zoom limit to the telephoto end is called the xe2x80x98telephoto limitxe2x80x99 or the xe2x80x98tele position.xe2x80x99 The zoom limit to the wide-angle end is called the xe2x80x98wide-angle limitxe2x80x99 or the xe2x80x98wide position.xe2x80x99 When the camera is turned off, the zoom lens barrel is automatically controlled to take the barrel retracted position.
For driving the zoom lens, the zoom lens barrel must be controlled to stop precisely at the zoom limit positions and not to move beyond them. However, it is undesirable to stop the zoom lens barrel by abutting it against a stopper, because this applies a load to the motor that is driving the zoom lens barrel. Therefore, position markers are provided at the zoom limit positions of the wide-angle and telephoto ends. And a controller of the camera stops the lens barrel when it detects the markers while driving the lens barrel.
The relative movement of the lens barrel is detected by counting pulse signals that are produced according to the movement of the lens barrel. Since the lens barrel moves back and forth within the zoom range, backlash of the motor and the driving mechanism of the lens barrel may cause count errors. The counted number may suggest a wrong position of the lens barrel. Therefore, the lens barrel position is directly detected to correct positional deviation. Compared with the relative lens barrel position detected by counting pulse signals, the position that is directly detected is called the xe2x80x98absolute position.xe2x80x99
Proposed technologies relating to the position control of the lens barrel include, for instance, a technique described in Japanese Laid-Open Patent No. H05-181050 filed by the present applicant. This technique uses a pulse generator mechanism for generating pulses to detect the displacement of the focal length of the photographic optical system, a counter for counting pulses generated by the pulse generator mechanism, and a position detector mechanism for directly detecting the wide-angle and telephoto ends of the photographic optical system. Here, the output of the position detector mechanism is used to correct the counted pulse number, and thus, correct any discrepancy between the counted pulse number and the actual lens barrel position, enabling accurate position control. A camera with this technique detects the absolute position of a lens barrel that moves between the wide-angle and telephoto ends and controls the movement between them using a pulse count. In other words, absolute positions are determined within the moving range between the wide-angle and telephoto ends, and read patterns for correcting the pulse count are applied there. When the zoom lens barrel passes the absolute positions, the pulse number counted for detecting the position is corrected (increased or decreased), if necessary, to a correct pulse number to cancel any error that occurs by then and to obtain the correct position.
Manufacturers should provide a lineup of cameras having a variety of zoom specifications according to the users"" preferences in order to meet their requirements and to induce them to purchase.
Manufacturers design and produce many different types of photographic lenses having different zoom specifications. If the different types of photographic lenses have a totally different structure and control mechanism, each requires certain design processes and financing for production equipment, influencing the production costs of the cameras.
It is preferred that as many common parts as possible be used to produce cameras with multiple zoom specifications, in order to reduce production costs.
It is an objective of the present invention to provide a camera having multiple zoom specifications at low cost by using the same zoom lens barrel.
The present invention discloses a technique that allows a common zoom lens barrel to be used in cameras having different zoom specifications, thereby lowering production costs. The cameras have an optical zoom system with a variable focal length from the wide-angle end to telephoto end by moving the zoom lens barrel from the wide-angle end to telephoto end.
The camera has a zoom lens barrel for changing the focal length of a photographic optical system, a zooming part for driving the zoom lens barrel, a pulse generator part for generating pulse signals according to the movement of the zoom lens barrel, a counter part for increasing or decreasing the pulse number of the pulse signals according to the moving direction of the zoom lens barrel, a position detection part for detecting when the zoom lens barrel is at certain (predetermined) positions, and a control for controlling the zooming part to prevent the zoom lens barrel from moving beyond the zoom limit.
The control determines when the zoom lens barrel is at one of the certain (predetermined) positions that is the closest to the zoom limit within the zoom range. After this detection, the control controls the zoom lens barrel to stop when a certain number of pluses are counted that corresponds the movement from the closest certain position to the zoom limit.
It is preferred that a memory that stores the pulse number for the closest certain position and the certain number of pulses or information from which these are induced is provided and the control performs controls based on the stored information.